This invention relates to the nuclear reactor art and to the art of separating isotopes. It has particular relationship to the separation of isotopes of zirconium for the purpose of improving the efficiency of nuclear reactors by reducing the absorption of neutrons by parts of nuclear reactors such as cladding, thimble tubes, grids, pressure tubes, fuel plates, cladding liners and the like. Feichtner discloses that the neutron absorption cross section of nuclear reactor parts composed of zirconium may be improved by forming the parts of zirconium substantially enriched in a low neutron-absorption isotope, such as .sup.90 Zr, or of zirconium depleted in a high neutron-absorption isotope, such as .sup.91 Zr. The enrichment or depletion is achieved by selectively irradiating vapor of material formed of a compound or compounds of zirconium with a laser beam tuned to the vibration frequency of a chemical bond of the component of the material including the selected isotope, which is here designated as .sup.s Zr, or of a bond linked directly or indirectly to .sup.s Zr. Zirconium compounds suitable for processing with a laser beam must have a number of properties which adapt them to this processing. The compounds must be capable of being rendered volatile within a moderately elevated temperature range. Typically this temperature range is between 100.degree. C. and 200.degree. C. Within this temperature range the compounds must have substantial vapor pressure, also the compounds must not be susceptible to thermal decomposition. In particular the compounds must not be decomposed at a temperature below the upper limit of the temperature range at which they are volatilized. The compounds must not be susceptible to hydrolysis. Hydrolyzed compounds are not volatile and are usually present in a form, for example particulated, in which they are not suitable for processing so as to enrich them or deplete them in an isotope. The difficulty and cost of preparation of the compounds is also an important consideration. An indispensible requirement is that the compounds must have accessible chemical bonds whose vibrations are within the frequency range of lasers operating at emitting rates and intensities at which appreciable quantities of selected isotopes are produced. Typically these lasers are of the carbon dioxide type which operate in the infrared range at about 1000 cm.sup.-1 wave number. For more complex bonds at lower frequencies a Raman-shifted carbon dioxide laser operating between 450 and 700 cm.sup.-1 wave number may be used.
Feichtner discloses separation of the isotopes of zirconium using the alkoxide compounds, zirconium tetra tertiary butoxide, zirconium tetra tertiary amyloxides and zirconium tetra isopropoxide. These compounds are highly satisfactory, but they are subject to hydrolysis. In using these compounds provision must be made to prevent the penetration of moisture into the chambers in which these compounds are volatilized and excited.
It is an object of this invention to overcome this disadvantage of the process taught by Feichtner and to provide a method of separating isotopes in whose practice compounds, which meet the above stated requirements and in particular are not appreciably subject to hydrolysis, shall be used.